Resistance unit



Oct. 31, 1939. s. c. McKEOWN RESISTANCE UNIT Filed April 7, 1937 K, 4L2, ATTOR Pat ent ed Oct. 31, 1939 UNITED STATES PATENT" OFFICE v slgnor to Ward corporation of New York Electric Company, a

Application April '2'. 15:1. Serial No. 135.401 5 Claims. (01. 201-83) This application relates to resistance'units having a resistor especially adapted for use in electric circuits where the current to be carried by the resistive element is comparatively large. I

One of the main objects of the invention J30 produce a resistance unit of skeletonizeti form wherein the resistor is supported in such manner that there is a maximum dissipation of heat to the air and a minimum conduction of heat to the supporting parts. Another object is to support the resistor rigidly so that it will maintainits position throughout its length even when heated to a comparatively high temperature and avoid any possibility of the adjacent turns contacting with each other. Another object is to provide a simple form of construction and permitthe unit to be conveniently assembled. Another object is to provide means for making connection to the resistor at the ends and at any intermediate points by the user, thus affording adjustment of the resistance to be included in any circuit and also permitting any desired number of tap connections to be made. Another object is to secure adequate and firm electrical connection between the resistor and the outside circuit in a convenient manner. Other objects and advantages will be understood from the following description and accompanying drawing illustrating a preferred embodiment.

Fig. 1 is a side view 01' the complete unit;' Figs. 2 to 6 are enlarged views, Fig. 2 being an end View, Fig. 3 a section on the line M iii Fig. Q, Fig. 4 a section of the clamp on the line 4-4 or Fig. ,2, Fig. 5 a perspective view of one of the insulating supporting elements and Fig. 6 a perspective view of modified form of supporting bar. Referring to Figs. 1, 2 and 3; the resistive conductor I is shown as forming aoirculal'q coil with the adjacent turns spaced apart uniformly in i order to form a coil of uniform pitch. The resistor is bare wire and may be inade elfiron, nickel-chromium and various other metaispand alloys. The main support oi the uhit is a bar 2 which extends lengthwise through the coil and projects beyond its ends, and is shown as having notches 3 on one side of the bar near its outer ends for positioning the unit on any suitable support. The bar is shown of square cross-section.

In order to support the resistive conductor in spaced position from the bar, there is provided a series of insulating elements 4 shown in the form of discs. These discs, as shown in Fig. 5,. have a central opening 5 of the same shape as the bar I and are adapted to slide freely on the-bar tor-the purpose of assembling. The rounded corners of the opening 5 are for the purpose of avoiding any tendency of the disc to crack at the corners. These discs are preferably made of unglazed porcelain but may be made of any suitable insulating mat'erialthat will withstand heat. 0n the outer rim of each disc, at diametrically opposite points, as shown in Fig. 5, are formed rounded projections 1 extending in an axial direction. Each of these projections carry an additional outwardly extendlng projection O which extends in a circumferential' direction. These projections or lips 8 are rounded on their outer surface and sides and converge toward each other outwardly, giving them the general shape of a wedge. The width of the base is equal to or less than the space between the tii'rns of the resistance coil, while the outer portion of the projection 8 is reduced and rounded surficiently to accommodate itself to the pitch oi. the resistance coil.

The insulating discs are positioned on the bar 2 in widely spaced relationship, as shown in Figs. 1 and 3 and iorm supports for the resistive conductor at spaced points only. This permits the intervening portions of the resistor to be surrounded by air, not only externally but also internail'y in the space between the conductor and the supporting bar. Moreover, the resistor is spaced from the outer surfaces of the insulating discs except where it engages the outermost points of the rounded projections l and the sides of the lips-8. Thus the resistor is exposed to the air for ready heat dissipation throughout the entire length except where it makes contact at the few points on the projections I and 8.

In assembling the unit, the insulating discs are positioned on the supporting bar in spaced relationship and then the resistance coil is placed with one end against the outermost disc 8 and threaded onto the first disc, diametrically opposite projections 8 on each disc being axially displaced the distance of half the pitch of the coil, as shown in 1 and 3. Thus when the coil is threaded onto the first disc, the two opposite projecting lips form small portions of a thread corresponding to the pitch of the coil. The square section of the supporting bar and the square holes through the disc prevent the discs from turning as the coil is threaded thereon. After the coil has been threaded some distance on the first disc, it engages the second disc in its properly spaced position and then as the coil is turned, it engages the third disc and so on until the entire coil is threaded into position as shown in Fig. l. A supporting disc ispreferably located at each end of the coil, as shown in Fig. 1 and is preferably fixed in position on the bar, as'by cotter pins 9 at its sides passing through the bar, as well shown in Fig. 3. These pins prevent the coil and discs from shifting along the length of the bar. With the end discs locked into position, it will be apparent that the intermediate discs are necessarily fixed in their initial positions because they cannot turn on the supporting bar and the projections 8 prevent them from shifting axially with reference to the coil.

It will be noted from Fig. 1 that each successive insulating disc is mounted on the bar so as to bring its projections 8 in an axial plane at rightangles to the axial plane of the adjoining insulating discs. That is, one series of alternate discs support the coil at upper and lower points. while the other series of alternate discs support the coil at the two sides. This gives a much more rigid support to the coil than would be the case if the discs were positioned so as to support the coil only at top and bottom points. If desired, each insulating disc may be provided with more than two projections 8 spaced circumferentially from each other and spaced axially to conform to the pitch of the coil but it has been found in practice that two projections are ordinarily sufficient when the successive discs are mounted to form supporting points in planes at right-angles to those of the adjoinin discs.

Instead of using a wire of a circular crosssection as the resistive conductor, a wire of square cross-section may be used, or of rectangular form wound edge-wise, or of any other desired crosssection. Also, instead of using a solid main supporting bar of square cross-section, as shown in Figs. 1, 2 and 3, the bar may be in the form of a channel iron It, as shown in Fig. 6, or the supporting bar may be of any desired form of cross-section with the opening in the insulating discs conforming thereto, so long as the shape is such as to prevent the insulating discs from tuming on the bar.

Referring now to the means for making connections to any part of the resistive conductor from an external circuit, this comprises a pair of plates ll, l2, preferably of sheet metal. These plates extend in a circumferential direction and are provided at their inner ends with opposed faces having outwardly extending portions l3 adapted to embrace the outer portions of the conductor and having inwardly extending portions l4 adapted ,to engage the inner portions of the conductor. Thus the inner part of the clamp forms a space of substantially square crosssection, as shown in Fig. 4 and extends in a circumferential direction around the conductor so as to form a considerable contact engagement for securing good electrical connection. By making the clamping space or square or similar formation, the terminal is adapted to clamp conductors of different sizes within range. Through the outer portions of the plates are passed clamping screws l5 having a threaded engagement with one of the plates H as well shown in Figs. 3 and 4. The plate I2 is formed with outwardly pressed rims 96 around the screw openings to form means for obtaining a longer threaded engagement with the plate l2 by the screws l5. Between the plates where the outer central screw l5 passes, is a washer i! for spacing apart the outer portions of the plates in order to insure a more effective clamping of the conductor by the inner portions of the plates. The outer screw it may be provided with extra washers is under its head for clamping the external conductor between airman them for forming connection to an external cirsuit.

it is evident that this form of clamp can be located on any portion of the exposed conductor between the insulating discs and can also be applied to the conductor at the outside of the insulating discs in certain positions. For this purpose the clamping plates have a cut-away central inner recess i8, as shown in Fig. 2 so that, if desired, the clamp can be bridged over any one of the projections I and 8 where they occur on the insulating discs and can of course be readily applied to the conductor over the discs where these projections are not located, thus giving a permissible location of the clamps over the discs in different positions along the coil at approximately apart.

Although a preferred embodiment of this invention has been described, various modifications may be made without departing from the scope thereof.

I claim:

1. A resistance unit comprising a coiled resistive conductor with adjacent turns spaced from each other, a central supporting bar within the coil, and a plurality of insulating discs spaced apart from each other mounted on said bar within the coil and supporting said conductor, said discs having projecting portions extending in an axial direction with reference to the conductor coil for supporting and spacing said conductor from the outer surface of said discs.

2. A resistance unit comprising a coiled resistive conductor with adjacent turns spaced from each other, a central supporting bar within the coil, and a plurality of insulating discs spaced apart from each other mounted on said bar within the coil and supporting said conductor, said discs having projecting portions extending in an axial direction with reference to the conductor coil for supporting and spacing the conductor from the outer surface of the discs and having projections extending outwardly from said projecing portions and between turns of said conductor.

3. A resistance unit comprising a coiled resistive conductor with adjacent turns spaced from each other, a central supporting bar within the coil, and a plurality of insulating discs spaced apart from each other mounted on said bar within the coil and sup orting said conductor, said discs having external projecting portions extending in an axial direction with reference to the conductor coil for supporting and spacing the conductor from the outer surface of the discs, said projecting portions being formed to engage and support the conductor at only a substantially point contact.

4. A resistance unit comprising a coiled resistive conductor with adjacent turns spaced from each other, a central supporting bar within the coil, and a plurality of insulating discs spaced apart from each other mounted on said bar within the coil and supporting said conductor, said discs having external projecting portions extending in an axial direction with reference to the conductor coil for supporting and spacing the conductor from the outer surface of the discs and having projections extending outwardly from said projecting portions and between turns of i said conductor, said projections being of a gen eral wedge-shape form.

5. A resistance unit comprising a coiled resistive conductor with adjacent turns spaced from each other, a central supporting bar within the coil, a plurality of discs spaced apart from each other mounted on said bar within the coil and supporting said conductor. said discs having external projecting portions extending in an axial direction with reference to the conductor coil for supporting and spacing said conductor from the outer surface of said discs, and a terminal for clamping opposite sides of v84 circumferential portion of said conductor comprising a pair 

